Like the previous games in the series, Global Offensive is an objective-based multiplayer first-person shooter. Each player joins either the Terrorist or Counter-Terrorist team and attempts to complete objectives or eliminate the enemy team. The game operates in short rounds that end when all players on one side are dead or a team's objective is completed. For most game modes, once a player dies, they must wait until the round ends to respawn.

Players purchase weapons and equipment at the beginning of every round with money awarded based on their performance. Completing objectives or killing enemies earns the player money while negative actions, killing a teammate or hostage, takes money away from the player. In addition, when a round ends all players receive some amount of money, with players on the winning team receiving substantially more.

Counter-Strike: Global Offensive adds new weapons and equipment not seen in previous installments, most notably the firebomb for each side (referred to as a Molotov on the terrorist side and as an Incendiary Grenade on the Counter-Terrorist side). These temporarily cover a small area in fire, dealing damage to anyone passing through.

Game modes
Currently, Global Offensive features five game modes for online play:

Classic Casual and Competitive: Counter-Strike's most played game mode, both involving Bomb Scenario and Hostage Scenario missions. At the start of each round, players can purchase weapons and gear with money earned from various actions, from assisting on kills to completing objectives. Regardless of mission type, a round ends when one team completes an objective, eliminates the other team, or lets the timer run out. If the timer runs out before one of these objectives are completed, the team which did not need to complete an objective wins.

Bomb Scenario: the Terrorists must plant a C4 explosive at one of two designated bombsites and protect it until its countdown finishes and detonates; the Counter-Terrorists must prevent the bomb from exploding, either ensuring that the terrorist team does not plant it or defusing it once it is planted. If the CT team does defuse it, the CT team will still win regardless how many enemy team members are still alive.

Hostage Scenario: the Counter-Terrorists must rescue hostages from the Terrorists, and bring them to an extraction point; the Terrorists must prevent the hostages from escaping. If a Terrorist or Counter-Terrorist attempts to kill hostage, they will suffer a heavy cash penalty. An update later changed how Counter-Terrorists rescue hostages: instead of leading them around, players must carry one hostage at a time to the extraction point.

Arms Race: a deathmatch-based mode where each player is rewarded for every 2 kills with a new weapon, or every 1 kill if they kill the enemy leader. The first player to get a kill with the golden knife, the final weapon on the list, wins the game.

Demolition: a round-based mode that removes weapon and equipment purchasing, instead rewarding players who manage at least one kill by giving the next weapon in a predetermined set of weapons. After a second kill with that weapon the players are also rewarded a grenade along with their new weapon for the next round. This is something similar to the bomb scenario mission, which also requires one of the team to detonate the bomb site. But un the casual ones, these have only one bomb site.

Deathmatch (added on November 12, 2012): a mode consisting of 10-minute matches. Players must gain the highest possible score by earning kills with different weapons or desired weapons. The number of points from a kill depends on the weapon. Players may also take advantage of bonus timers for different weapons, or using knife to score extra points. Like in Arms Race, players automatically respawn after being killed, but also when they choose to respawn with bonus weapons.

Global Offensive also offers two offline modes: Offline with Bots, which offers the same game modes with AI-controlled bots; and a Weapons Course, a single player map serving as a tutorial and a training mode.